Multi-Path Transmission Control Protocol

The TCP (Transmission Control Protocol) transport protocol occupies a hegemonic position within Internet communications, particularly given the predominance of HTTP (Hyper Text Transfer Protocol) connections used to access web server content. However, TCP can only establish a connection between two terminals via a single path, regardless of the number of paths actually available to enable these terminals to communicate with each other.

With the development of multi-interface terminal ranges capable of operating several logical interfaces associated with one or more physical interfaces, several IP addresses can be assigned to these interfaces, so that these terminals can connect simultaneously or not, depending on whether they are in motion or not, to different types of network (e.g. fixed network, mobile network, wireless network including WLAN, etc.). These IP addresses may belong to the same family or to different families (IPv4, IPv6 or both). They can have different lifespans and scopes (e.g. private IPv4 address, unique local IPv6 address (ULA), global IPv6 address (GUA). These addresses can also be assigned to the same logical network interface or to different interfaces.

Despite the availability of these new resources, capable of exploiting different networks and therefore different paths to communicate with a remote terminal, a TCP connection, typical of a website consultation for example, will always be established over a single path.

The emergence of these multi-interface terminals, with several interfaces connecting to different networks, introduces a degree of frustration when it comes to optimizing the use of resources available to establish a communication between two terminals. Indeed, since TCP connections are identified by an IP address and a port number, any modification of this identification information is likely to penalize the operation of a TCP connection in progress, with the risk of abruptly interrupting the communication service based on the TCP connection.

Thus, a change of address (or port number) is particularly damaging when the terminal is assigned a new IP address, or because it connects to another network, or when the interface to which the IP address is associated is no longer available (e.g. due to an expired lease). Means of informing the remote TCP correspondent that an IP address is no longer valid are then required to ensure that an existing connection is maintained (for example, in the case of long-duration TCP sessions).

It is important to note that a terminal's support for multiple interfaces is volatile, as the ability to use these interfaces depends in particular on the conditions of connection to the network(s) at the terminal's location, and on...